Simelane had been released unsupervised, despite warning signs over the state of his mental health while in prison.

Christina, a pupil at Leasowes High School in Halesowen, was pronounced dead at the scene after being stabbed in the chest on the upper deck of a bus in Birmingham at about 7.30am on March 7.

Her family made it clear that questions remained over why Simelane had not been supervised after his release from jail at the end of 2012.

Giving the facts of the case, prosecutor Peter Grieves-Smith said: "On March 7, Christina Edkins boarded a bus to go to school and she went to the upper deck and sat in a seat. Also on the upper deck was the defendant."

Simelane boarded the bus at 5am, and had been reported by another passenger for sleeping on the back seat.

When challenged by the driver, he produced a valid travel pass although it was later revealed this did not belong to him.

Mr Grieves-Smith said: "He was carrying a white plastic bag and the CCTV shows his top bearing a distinctive animal print logo. In his bag is what the prosecution say was a knife, 10 to 12 inches in length.

"Christina Edkins boarded just after 7.30am and went upstairs and sat on her own. Within seconds the defendant got up and moved forwards three seats and pulled out the knife, which he then hid."

Simelane then got up and walked forward towards where Christina was sitting, "leant closer to her", stabbed her and started to walk off, the court heard.

"Such was the the nature of the attack, nobody else on the upper deck realised what had happened until Christina reacted," Mr Grieves-Smith said.

The teenager’s parents, Jason and Kathleen Edkins and siblings Ryan and Joanne said in a statement that they were still struggling to come to terms with the loss of their “beautiful, bright, caring girl”.

Her great uncle Chris Melia added that if 23-year-old Simelane had been properly monitored after his release, the attack on the top deck of the No 9 bus on the morning of March 7, would not have happened.

Mrs Edkins said their daughter came from "an ordinary, quiet and hard-working family" and was "loved by everyone".

It was her caring nature that lent a desire to become a nurse or a midwife, Mr and Mrs Edkins said.

They also revealed the pride in finding out she had passed 11 GCSEs, tempered with the bittersweet knowledge she was not there to open her own results letter.

In a statement, her family said they had been pulled apart by the "horror, distress and pain" of Simelane's devastating crime.

They said: "The loss of a child is the worst thing that can happen, made even more grievous by such a senseless crime.

"The family are all innocent victims and must pay the penalty as we stand helplessly by and watch the lives of the people we love shattered like glass, knowing we can never put the fragile pieces back together."

Welcoming the outcome of the court hearing, the family said it would "bring an element of resolution in that the sentence passed means the public is protected from this man".

They added: "However, he was allowed the freedom not only to take the life of an innocent child but, in doing so, to ensure the lives of the people whom she loved are forever affected as a result of his crime."

Despite the family's loss, Mr Melia said there was "no feeling of vengeance or retribution" toward Simelane.

"It's just a matter of 'get him out of society'," he added.

Outlining Simelane's psychiatric history, Mr Grieves-Smith said the defendant had been heard making threats against two schoolgirls on a bus around a year before the stabbing.

Born in Swaziland, Simelane received a reprimand for possessing a knife in 2007 when he was 17, having suffered mental health problems since his mid-teens.

Simelane was cautioned for an offence of battery two years later and given a conditional discharge for criminal damage in May last year.

Other offences, including an assault on a police officer and an incident in which he threatened his mother with a knife, saw Simelane made the subject of a restraining order and jailed for 26 weeks in July last year.

A week after his release from prison last October, Simelane was jailed again, receiving a four-week term for vehicle interference.

Birmingham and Solihull Mental Health NHS Foundation Trust which treated Simelane while he was in prison last year is currently carrying out a review into the incident and is expected to publish a report in December.

In a statement, a spokesman for the Trust said: "We would like to offer our sincere condolences to Christina’s family for what was an unprovoked attack on an innocent member of the public.

"Phillip Simelane had previously been in receipt of care from a number of healthcare providers over a period of years.

"Our Trust’s involvement was in the form of prison-based mental health assessments during a prison term for an unrelated offence in 2012.

"What is clear, is that there are lessons to be learned for us and others involved in the care of Phillip Simelane to prevent such a tragedy happening again in the future.

"As a Trust we are currently leading an external review, commissioned by Birmingham Cross City Clinical Commissioning Group, on behalf of all the parties involved and intend to report on our findings in December 2013.

"We would not want to speculate on the outcome of this review, but we are clear that this will be an externally reviewed, thorough investigation and we will seek to learn from and fully implement these findings across the healthcare providers involved."